Resistor and method of making same



April 29, 1930. s, o w 1,756,368

RESISTOR AND METHOD OF MAKING SAME Filed Sept. 2, 1925 hue/7w): 5/3 mz nal L 027)? Patented 'Apr. 29, 1930 UNITED STATES SIEGMUND LOEWE, OF BERLIN, GERMANY, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE RESISTOR AND METHOD OF MAKING SAME Application filed. September 2, 1925, Serial No. 54,081, and in Germany November 6, 1924.

, This invention relates to electrical resistances especially for wireless telegraphy and telephony, including broadcasting, and a new art of making same.

In the following there is described a method of making high-resistance units, according to which resistances may be manufactured, which meet all requirements for this purpose. These requirementsare as follows:

(1) Complete absenceof the so-called afte'r-effects, which consist in residue-charges after switching ed the current.

(2) Independence of the resistance from the voltage impressed thereupon.

l (3) Complete absence of all contact and thermo-potentials.

(4:) Tnsensitiveness in a mechanical way.

(5) Resistivity against heating upon temperatures up to about 400 degrees (Celsius).

29 (6) Absolute reliability of the contacts between the high-resistance layer and the leading-in electrodes.

.(7) Easy manufacture of resistances having a prescribed resistance value.

(8) Especial cheapness of manufacture.

The invention is illustrated in the figures of the drawing in which Figs. 1 to 3 show steps in the manufacture of a resistor, and

Figs. l and 5 show two modifications of completed resistances made according to the invention.

According to this invention the resistance is made as follows:

There are first provided, as Fig. 1* shows, two wires of platinum or of a substitute of platinum or the like, provided at their ends with small spirals. There are furthermore provided cut round glass rods. These three elements are designated in Fig. 1 with the letters a, b and c. The spirals of the pieces a and c are thereupon placed upon the glass rod and the ends of the latter are exposed to a gas-flame or the like. The glass rod will thus slightly be thickened at its ends and thereby will be firmly placed into the windings'of the spiral. The wire itself, however, will remain at the surface of the glass rod. A resistance carrier made in this manner is shown in Fig. 1. In order to make the resistance layer proper, experiments have shown, that the following processis especially well suited.

Chinese drawing ink in ordinary condition is poorly conductive. After drying, however, it will lose its conductivity almost completely. If, however, Chinese drawing ink is heated to a temperature of from 250 to 300 (Celsius), the layer will again become conductive. This layer in distinction to soot or graphite will have the advantage of firmly sticking to the surface of the glass. Tf now concentrated Chinese drawing ink is heated to some degree, there will be obtained an extraordinarily well conducting layer, so that resistance values down to several thousands of ohms may be produced. If the Chinese drawing ink is thinned for instance with alcohol, the thickness of the generated layer may be reduced at will and thus the conductivity of the same may be extraordinarily reduced.

According to this invention, now, the property of concentrated Chinese drawing ink to form highly conductive layers is used for the purpose of efliciently securing the contact between the leading-in wires and the resistance layer proper. According to this, during the further manufacture, a coating of concentrated Chinese drawing ink is applied upon the spirals which are molten into the glass rod, as indicated in Fig. 2 of the draw in g. Upon applying heat to the ends of said glass rod, end caps will he produced, which possess a Very high conductivity and which are very intimately connected with the spirally shaped electrodes. The resistance body proper is now made by depositing a layer of Chinese drawing ink which is thinned for instance by alcohol. This layer also will be rendered conductive only after heating the same.

The most suitable process of manufacture has been found to consist of bringing the glass rod above the open end of a tube, through which a stream of air is passed, as shown in Fig. 3 by the arrows, said stream of air being heated by means of a heating spiral provided within the interior of the tube. The thinned solution of Chinese drawing ink is now deposited upon the hot glasscarrier by means of a spraying device, the

said carrier during this process being mounted within a holder or the like and kept in continuous rotationby means of a motor, by having, for instance a pulley and a driving string interposed. On its other end the glass rod rests upon a resilient fork, which at the same time acts as a second leading-in electrode. It is now preferable, to connect a battery and a galvanometer to the fork and the rotating carrier, in order to be able to observe the adjustment of the resistance value. It will then easily be possible to observe the adjustment of the resistance value,

' by considering, that by reason of the high above-enumerated requirements.

temperature the conductivity appears to be greater than in cold condition.-It is always .easy to find the factor by which the value of the resistance will thus be changed, so that one will be in a position to exactly and systematically manufacture resistances of any desired value. The resistances made according to this process will comply with all These resistances, however, are at first hygroscopic. It is therefore preferable to dip the resistance bodies, which are thus made, into parafline which is free of water. Thus the carrier will be caused to be covered up by a tightly closing layer of parafiine, which will render the resistance completely insensitive I against any further influences due to moisture. Advantageously the resistance thus made is either molten into a glass tube and provided with terminal caps, or as shown in Fig. 4 brought into an insulating casing with connecting screws and completely surrounded by para-fine. The parafline is indicated by a light shading inthe drawing. A resistance of this kind is completely insensitive against mechanical shocks and electrical stresses. Protective substances other than paraffine may be used. Some such substances are kolophonium, shellac, and sulphur.

It is of especial importance, that the resistance bodies thus made may be enclosed into an evacuated space and that they may sustain a high temperature, without losing their conductivity. These resistances are therefore well suited for being mounted within a highly evacuated tube.

Another'form of resistance according to this invention is shown in Fig. 5. In this case the resistance carrier is bent in semi-circular form and provided with a number of taps, which lead to the contacts of a rotary switch. The resistance body in this case is again made in the above-described manner. This form of resistance results in a variable highresistance unit, such as may be used for many purposes in electrical engineering. Preferably also this form of resistance is mounted within a casing of porcelain or pressed ma- In this case the contact terminals may be provided with essentially thicker coatings, whereby also the contact with the leading-in electrodes may be rendered more perfect. These resistances may also be mounted within vacuum tubes, and preferably the latter also I within an evacuated casing.

I claim:

1. A method of making. a hi h resistance member adapted to withstand aliigh temperature without losing its resistivity which consists in first fusing the spiral ends of a pair of electrodes to the surface of the ends of a glass rod, then coating said fused ends with a-ooncentrated layer of Chinese drawing ink, heating said coated ends, then supporting said rod at the electrodes and rotating the former, simultaneously directing a stream of heated air over the surface of said rod and spraying a thinned solution ofChinese drawing ink on said surface to a predetermined resistance value, coating said unit with a pro tective substance, and finally encasing said protectively coated unit in an insulating casing.

2. A method of making a high resistance member adapted to withstand a high temperature without losing its resistivity which consists in affixing the ends'of a pair of electrodes to the surfaces of the ends of a non-conductive carrier, then coating said ends with a concentrated layer of Chinese drawing ink, then supporting said carrier at the'electrodes and rotating the former, simultaneously directing a stream of heated air over the surface of said carrier and spraying a thinned solution of Chinese drawing ink on said surface to a predetermined resistance value, coating said unit with a protective substance, and finally encasing said protectively coated unit in an insulating casing.

3. A method of making a high resistance unit adapted to withstand a high temperature without losing its resistivity which consists in first affixing a pair of electrodes to the ends of a fusible, non-conductive carrier, then coating said ends with a concentrated layer of carbonaceous liquid, then supporting said rod at the electrodes and rotating the former, and simultaneously directing a stream of heated air over the surface of said carrier and spraying a thinned solution of Chinese drawing ink onlsaid surface to a predetermined resistance va ue.

4. A method of making a high resistance member adapted to withstand a high temperature without losing its resistivity which consists in affixing the ends of a pair of electrodes to the ends of a carrier, then coating said fused ends with a concentrated layer of carbonaceous liquid, heating said coated ends, then rotating the carrier, simultaneously directing a stream of heated air over the surface of said rod and spraying a thinned solik, tion of the same liquid on said surface to a predetermined resistance value, coatin said unit with a protective substance, and ally encasing said protectively coated unit in an insulating casing.

5. A high resistance member adapted to Withstand high temperature without losing its resistivity comprising an insulating casing, a resistance unit enclosed in said casing and surrounded by parafline, said unit including a non-conductive rod having the spiralled end of a metallic conductor attached to the surface of each end of said rod, said rod ends being provided with a coating of a concentrated resistance material, the surface between said ends being provided with a less concentrated coating of said material.

6. A high resistance member adapted to withstand high temperature without losing its resistivity comprising an insulating casing, a resistance unit enclosed in said casing and surrounded by a protective substance, said unit including a carrier having the spiralled end of a conductor attached to each end of said rod, said rod ends being provided with a coating of concentrated carbonaceous liquid, the surface between said ends being provided with a less concentrated coating of said liquid.

7. A high resistance member adapted to withstand high temperature without losing its resistivity comprising an insulating casing, a resistance unit enclosed in said casing, said unit including a carrier having the spiralled end of a metallic conductor attached to each end of said rod, said rod ends being provided with a coating of concentrated ink, the surface between said ends being provided with a coating of less concentrated ink.

8. A high resistance unit adapted to withstand high temperature without losing its resistivity including a non-conductive rod having the .spiralled end of a metallic conductor attached to the surface of each end of said rod, said rod ends being provided with a coating of a concentrated resistance material, the surface of said rod between said ends being provided with a less concentrated coating of said resistance material.

In testimony whereof I have afixed my signature.

SIEGMUND LOIEWE. 

